Social media usernames are often regarded as mere technical identifiers, yet they are in fact sociolinguistic artifacts laden with identity meanings. This study aims to describe the linguistic forms of social media usernames, analyze the self-identity constructions represented within them, identify the social factors influencing username selection, and compare identity construction patterns between students and teachers. The study was conducted at SMP Negeri 1 Batang-Batang, Sumenep, Madura, employing a mixed-methods descriptive approach grounded in the social constructivism paradigm. Data consisting of 175 usernames from 120 students and 55 teachers were collected through public profile documentation, semi-structured interviews, and limited participatory observation, then analyzed through linguistic classification, semantic analysis, and contextual analysis inspired by Critical Discourse Analysis. The findings reveal six linguistic username categories, with real names (26.9%) and name-number combinations (21.7%) being the most prevalent. Students tend to construct expressive, peer-oriented identities through Indonesian-English code-mixing and creative aliases, whereas teachers construct more formal and professional identities. Username selection is shaped by seven interacting social factors, including peer group influence, institutional norms, platform affordances, local Madurese cultural background, global media exposure, age, and religiosity.